X-ray studies, in conjunction with other work, are being addressed to a number of significant biological problems. Structural work is being carried out on a number of derivatives, salts and complexes of the ionophore, lasalocid A(X-537A). In particular different structures from solvents of differing polarity are being examined. Structural studies are also reported on the fluorescent probe, bis-ANS, and on morphine derivatives. The compound, 14-hydroxymorphinone, exists in two different forms which differ in color and in the nature of the intermolecular hydrogen bonding. The solid-state decomposition of nitrazepam, a pharmaceutical related to valium, is being investigated. Studies are also in progress on aspects of dipeptide conformation and energetics.